Proton NMR Spectroscopy of Human Focal Epilepsy at 4.1T (R01NS33919) Introduction: Up to 20% of focal epilepsy patients (about 400,000 in the USA) fail to respond to anti-epileptic medication. Fewer than one-third of these refractory patients are currently considered candidates for the highly effective surgery to resect the seizure focus because the presurgical evaluation is costly, inaccurate, and often invasive (thus risky). Methods: Using quantitative MRSI (Core Project I) and MRI (Core Project IV) methods, determine the sensitivity and specificity of 1H MRSI and MR volumetry compared to EEG, PET, ictal SPECT, and routine MRI at 1.5T. Results: Early studies indicate that 1H MRSI is much more sensitive and specific than PET, ictal SPECT, or routine 1.5T MRI. Volumetry at 1.5T is not as sensitive, but still contributes significant independent information. Discussion: The high sensitivity and specificity of noninvasive MRSI and MRI for localization of the epileptogenic seizure focus could reduce the cost and risk of presurgical evaluation and could qualify more refractory patients for effective surgical treatment. When the head gradient coil and rapid imaging are implemented (Core Projects IV and II), then volumetry at 4.1T will be routinely included in the protocol.